1. Field of the Invention
The present invention relates to alkaline batteries having a gel type negative electrode and more particularly to the improvement of a gelling agent for the gel type negative electrode.
2. Description of Related Art
As the gelling agent, crosslinked and branched type polyacrylic acids or sodium salts thereof have been generally used. The crosslinked and branched type polyacrylic acids uniformly disperse zinc particles in the gel type negative electrode due to the high viscosity of the acids (e.g., JP2-119053A). Furthermore, they increase contacts between zinc particles per se and between zinc particles and current collectors to enhance current collecting effect.
In order to inhibit corrosion of zinc and maintain the shelf stability of batteries, amalgamated zinc comprising zinc particles to which mercury is added has been used. The mercury added enhances the current collecting effect by increasing contacts between zinc particles per se and between zinc particles and current collectors. However, the amount of mercury contained in negative electrodes of batteries must be reduced for protection from environmental pollution. When mercury is removed from zinc particles, contacts between zinc particles decrease and if the batteries are subjected to continuous vibration or shock for a long time, zinc particles in the gel type negative electrode move to one side in the negative electrode to cause deterioration in current collecting effect. Moreover, when the batteries are discharged, the surface of zinc particles is converted to zinc oxide owing to the discharging reaction and the particles become smaller and, as a result, the current collecting effect is further deteriorated. Therefore, when the batteries are continuously subjected to vibration and shock for a long time while being discharged, the voltage abruptly drops and dischargeability deteriorates.